Material for nuclear spin tomography MRI or magnetic resonance imaging (prototype)

ABSTRACT

The subject invention pertains instruments for use in nuclear spin tomography comprising a metal alloy comprising aluminum, vanadium, and titanium. In a specific embodiment, the subject invention relates to cardiovascular stents which can exhibit a low incidence of artifacts and are viewable in a nuclear spin tomography unit. The subject invention also pertains to a method for processing instruments for use in nuclear spin tomography. Such processing can comprise application of a wet chemical etching solution. In a specific embodiment, the wet chemical etching solution can comprise three parts hydrochloric acid and two parts saltpeter acid.

[0001] The invention relates to the use of a material in claim 1 and a process in claims 3 and 5.

[0002] In today's stent technology it is desirable to use cardiovascular stents that are able to adequately prop open the vessel, that can be accurately positioned and that, and this is new—can be viewed with nuclear spin tomography. Traditional stents are made of stainless steel and show distinct image distortions, so called artifacts. These artifacts occur when materials with high magnetic susceptibility are used.

[0003] A goal of the invention is to show means by which the occurrence of artifacts in combination with the stents and nuclear spin tomography can be avoided.

[0004] The solution is recapitulated in claims 1 through 5.

[0005] An alloy of 3 percent aluminum by weight and 2.5 percent vanadium by weight, with the remainder being titanium, known as material TIA13V2.5 or material No. 3.7194 or 253.7195 (ASTM Grade 9), shows especially few image artifacts and has sufficient hardness to be suitable for interventional instruments used in nuclear spin tomography.

[0006] The above named alloy according to ASTM Grade 9 is harder than an alloy according to ASTM Grade 5 or ISO 3.765 or 3.7165. This would have the following components: 90% titanium, 6% aluminum, and 4% vanadium. The material is more flexible than the so-called ASTM grade 9 material and is therefore more suitable for expanding a stent with the help of a balloon catheter.

[0007] Materials that are made to be artifact free but created with tools containing magnetizing components after processing show an increase in screen artifacts which rubbed off the tools. A reduction of surface magnetism can be achieved through dipping in etching solutions which etches the materials the tools are made of. The rub-off from the tools is eliminated by the wet chemical etching solution. Such an etching solution that removes the iron impurities consists for example of 3 parts hydrochloric acid and 2 parts saltpeter acid and can be further reduced with additional parts water in the etching process.

[0008] Stents manufactured in the manner here described can be ideally observed in nuclear spin tomography units in magnetic flux density>1.0 Testa. It was possible, for example with an unexpanded stent having a diameter of 1 mm, that was balloon expanded to a diameter of 4 mm, to clearly see all the stent struts, the so-called strats. It was also possible to get a good look inside the expanded stent. So-called in-stent-restenose in the interior of the stent can be seen when a stent has been treated in this manner. 

We claim:
 1. Use of metal alloy TIA13V2.5 comprised of 3% aluminum by weight and 2.5% vanadium by weight with the remainder being titanium for the manufacture of cardiovascular stents that exhibit a low incidence of artifacts in a nuclear spin tomography unit.
 2. Use of metal alloy TiA16V4 comprised of 90% titanium by weight, 6% aluminum by weight, and 4% vanadium by weight for the manufacture of stents that are viewable with nuclear spin tomography.
 3. A process for handling cardiovascular stents made of material containing titanium, especially when the metal alloy in claim 1 is used, defined in that the stents that are processed with tools containing iron are treated with a wet chemical etching solution to remove the deleterious effects of said tools.
 4. A process under claim 3 for the treatment of stents according to claim 1, and defined as being comprised of an etching solution that consists of three parts hydrochloric acid and two parts saltpeter acid and possibly additional water.
 5. A process for the control of in-stent-restenosis and defined in that the stent is manufactured and treated according to at least one of the herein described claims, and nuclear spin tomography is used to view the inner lumen of the stent. 